AB-007 (also called loxistatin, E64d, EST or ((2S,3S)-trans-epoxysuccinyl-L-leucyl-amido-3-methylbutane ethyl ester) is an ethyl ester prodrug, 342.4 mol wt (MW), which is completely converted in vivo to its acid form E64c (also called loxistatin acid or Ep 475, 314.4 mol wt, which irreversibly inhibits proteases belonging to the cysteine protease class by covalently binding to sulfhydryl groups in the proteases' active sites.

Two hydroxylated metabolites of loxistatin (or E64d) have been observed:
This metabolism, or in vivo hydroxylation, can result in lowering the effective concentration of the drug and shortens its half life in vivo.
Cathepsin B is co-localized with beta amyloid (Aβ) in plaques of AD brains and is elevated in cerebrospinal fluid (CSF) of Alzheimer Disease (AD) patients. Also, age-related changes in cathepsin B expression are consistent with the late age of onset of Alzheimer's. These findings, among others, indicate a role for cathepsin B in AD.